The overhead contact lines (catenary cables, contact cables and flexible catenary spans) of an electrified railway affect both the height and strain of the contact suspension due to the shrinkage or expansion caused by variation in temperature and because of the elongation of elastic linear material caused by creep, wear of cable, etc., as well as the tilting of the supports due to long time use. These factors cause contact loss, and deteriorate the current-collecting capability of overhead contact lines, whilst increased strain could cause the breakage of overhead contact lines, which leads to operation faults of the overhead contact lines.
Overhead contact lines are arranged in sections. Each of the sections is called an anchor section, and is installed at both ends. In order to automatically keep a constant strain of the overhead contact lines, normally, strain compensation devices are provided at anchor points.
Existing strain compensation devices that are currently in use have mainly the following two forms.
1. Existing compensation devices set up on existing overhead contact lines (catenary cables, contact cables and flexible catenary spans) of an electrified railway are usually of the weights type, two kinds of which, namely pulley block and ratchet wheel are normally utilized. These two kinds of compensation devices have the advantages of having simple structures and high reliability in operation. However, they have also the disadvantages of being large in size, heavy in weight, ugly in appearance, and easy to swing and get struck in a strong wind. Another disadvantage is that they are expensive in terms of installation and maintenance. This is mainly caused by the need of supplementary structures to support, conduct and protect such compensation devices and the daily operation management and repair work involved. Particularly while reconstructing electrical contact lines and installing the weight in low and narrow spaces of, for example, an underground railway and an existing tunnel etc., it is necessary to expand the cross sections of the tunnel. This will result in significantly increasing the project quantities, disturbing the traffic, prolonging project time, and increasing project expenses. In a place of more complicated geological conditions, it is even hardly to carry out the project.
2. The flexible catenary span of electrified overhead contact lines is the horizontal support device of overhead contact lines suspension in a railway station yard with multiple tracks, which consists of supports situated along both sides of railway, horizontal catenary cables suspended from the support, upper and lower positioning cables and accessories which hold and connect them.
In order to improve the current-collecting capability of overhead contact lines and decrease operation maintenance of flexible catenary span, a compensation device is provided on upper and lower parts of the positioning cable. The compensation device may be basically adapted to the steadiness of the height of flexible catenary span, however, it has the disadvantages of being short in compensation anchor section, big in strain changes, small in elongation length, poor in performance.
The following several kinds of compensation devices existing in China and other countries do not have wide application due to their various disadvantages.
1. Compensation devices consisting of several cylindrical helical compression springs in series (for example: the elastic strain compensation device of Chinese Patent No. 200420025333.1, overhead contact lines elastic strain automatic compensation device of Chinese Patent No. 200510038827.2): since the force of cylindrical helical compression spring adopted is directly proportional to the travel, such compensation device can not ensure the constancy of strain of the overhead contact lines.
2. Hydraulic or pneumatic type compensation devices (such as: a hydraulic compensation device for electrified railway of Chinese Patent No. 03235102.X, a differential plunger hydraulic strain compensation device of Chinese Patent No. 03218606.1, a pneumatic strain compensation device for electrified railway of Chinese Patent No. 0023267.2): due to the loss of oil or air, continuously monitoring and maintaining, and refilling oil or air are necessary. Since oil or air leaks occur frequently, their costs are higher and application thereof is restricted.